The Slinky is a toy made of a coil of steel that slithers up and down steps, one half propelling the other demonstrating the physical laws of inertia (matter's propensity to keep moving in the same direction) and Hooke's law (its tendency to return to its original shape after being stretched).

The Slinky was invented by Richard James during World War II. While working at the Cramp Shipyard, the young Philadelphia engineer experimented with coil springs that he hoped to make into shock absorbers for fragile instruments. While he was sitting at his desk one day, a torsion spring fell down from a shelf above and "walked" across a pile of books. Thus, James later claimed that he had not really invented the Slinky but that it had "practically walked into my life." Shrewdly anticipating the public's fascination for this curiously self-propelling object, James and his wife Betty took out a $500.00 loan and made 400 springs, which they named "Slinky" (which implies stealthiness and sinuousness) after Betty searched the dictionary for an appropriate appellation.

In November of 1946, the couple set up their wares in a corner of Gimbel's New York department store. They sold all 400 Slinkies in ninety minutes, and many millions in following years. Slinkies are now made of both metal and plastics, with crimped edges to protect the user from injury. A Slinky is on exhibit in the collection at the Smithsonian Institution's National Museum of American History.